Stormwater is collected from various surfaces in urban environments and directed through various inlets to a stormwater collection network of pipes and then, often, deposited untreated into various receiving areas which are generally natural water bodies such as streams. rivers, lakes or the sea.
The stormwater collection network has to cope not only with stormwater but also a variety of debris, which ranges from gross material such as branches of trees, plastics containers, to smaller material such as sand and very fine material such as silt. Very often toxic or damaging substances such as orlanic wastes and heavy metals are also carried into the stormwater collection system. Thus oils may be collected from road surfaces and lead may be accumulated from surface depositions.
The collected debris causes difficulties in so far as causing visual pollution by the deposition of the gross debris into the natural water bodies. The accumulation of a great deal of sand and silt also causes problems in that natural waterways become clogged by the build-up of such material over-time, and additionally natural grasses and flora and fauna are adversely affected. Often toxic compounds such as heavy metals are carried by silt and as a result the build-up of silt is often toxic, having both short and long term ramifications to aquatic plant and animal life.
It has been recognised that the above is a problem and a variety of suggestions for the screening of debris from stormwater have been made and some have been implemented. Most of the very large debris is excluded from entry into the stormwater collection network by grates or bars or by reason of the size of inlet apertures, but medium size and fine debris passes through these screening devices.
There are some inherent problems with the design of apparatuses for the removal of debris from stormwater collection networks. One issue is cost in so far as the network of stormwater pipes is very extensive, and a great deal of debris is to be removed. Additionally there are quite large flows of stormwater and any filtration system should not impede the flow significantly otherwise flooding will occur. Flows of stormwater vary considerably and any filtration system should preferably be functional or at least not adversely affect the stormwater collections system at any of the expected flow rates. Additionally it is desirable that any apparatus fit together with existing stormwater management arrangements. Also desirable is that construction is simple and inexpensive and that it is inexpensive to clean and maintain.
It is known to use a vortex as a means for separation of solids in sewage lines and these vortexes assist in alleviating the tendency of blockage of static separation units by floatable solids. A vortex will tend to have the greatest velocity at its periphery and much lower velocities toward the centre of the vortex. as a result there tends to be a greater deposition of sediments and other non-floatable debris towards the centre of the vortex because velocity is such that the debris does not remain suspended. As a consequence separators using a vortex often have a collection container, or a take-off conduit below the centre of the vortex to remove sedimented material. The vortex is quite convenient as a means of removal of debris. because it allows for a longer transition time for floatable, a good proportion of which become waterlogged and therefore sink.
However not all debris settles, such as neutrally buoyant matter and some debris is too small and as a consequence for greater removal it is convenient to provide for a filter to filter the water that has been separated by the vortex. Not all stormwater separators that have a vortex will also include a filter. but these suffer the deficiency of permitting more debris through the separation plant One problem with providing a filtration means is the difficulty of having the filter mesh clogged as a result of high velocity particles lodging within the holes of the filter medium or with having floatables such as oils and greases foul up the holes of the filter.
It is necessary to remove debris from stormwater pollution separators from time to time, and separators almost invariably have some access for removal of the debris. Municipal bodies or contractors acting on their behalf are equipped in varying fashions to manage the clean-out of stormwater separators. What is desired is an efficient means of removal of both floatable and non-floatable pollution. In some municipal districts vacuum cleaners are provided that allows for removal of debris from a sump, however vacuum cleaners are not always available, and are relatively expensive to use on a routine basis. As a consequence it is desirable that stormwater separators use a bag or basket which can be lifted out of a sump of its respective separator and from which the majority of sinkables can be removed, and the bag or basket replaced in the sump. On the other hand it is desirable to minimise the cost of construction of these installation, and the addition of a filtration chamber separate from a separation chamber adds a considerable cost,
It can be appreciated that because each of the stormwater separators is a sizeable construction it is desirable to minimise the cost of these installations